Dispensers of washing agents for dishwashers are normally provided for delivery of at least two different washing agents, one usually in the form powder or of a tablet and the other in the form of a liquid. Also known are in any case dispensers provided for delivery of a liquid substance only.
For what is of specific interest herein, the body of the dispenser defines inside it a reservoir for containing the liquid washing agent, in an amount sufficient to perform a plurality of cycles of operation by the machine. The dispenser is moreover provided with means for dividing the total amount of liquid agent contained in the reservoir into doses in order to deliver them individually at the appropriate moment in the course of a treatment cycle.
Following upon use of the dishwasher, the reservoir must be periodically topped up and for this purpose it has a charging passage, generally shaped as a pipe that opens on the front of the body of the dispenser. The passage is provided for receiving at least partially a removable plug, of a generally cylindrical shape. The plug and the passage are provided with means for mutual coupling that enable the plug to be kept in a blocking position, in which the charging passage is hermetically closed. The plug can be turned manually by the user of the machine in order to bring the aforesaid coupling means into a respective condition of release, in which the plug itself can be removed from the passage. Once the plug has been removed, the charging passage can be used for adding new liquid washing agent in the reservoir.
In order to enable a hermetic closing of the tank, the plug is provided with an annular gasket, designed to co-operate with a corresponding sealing surface defined in the body of the dispenser, for example, within the charging passage. The coupling means, which are usually of the bayonet-coupling type or possibly of the threaded type, enable precise coupling and tightening of the plug with respect to the charging passage in such a way that the aforesaid gasket co-operates in an effective way with respect to the aforesaid sealing surface.
In the dispensers of the type indicated, the user—after removing the plug from the charging passage—must rest the plug itself somewhere, or else hold it in his hand: this fact renders the operations of topping-up of the reservoir with the liquid washing agent less convenient from the practical standpoint.
Also known are dispensers in which the passage for charging the reservoir with the liquid washing agent can be opened and closed by a hatch, instead of by a removable plug, said hatch being hinged to the body of the dispenser so as to be able to turn about a substantially horizontal axis, or in any case an axis substantially parallel to the front of the body of the dispenser. This hatch is equipped, on its internal face, with a seat for a sealing gasket, which is usually annular and is designed to co-operate in a fluid-tight way on a peripheral lip of the charging passage. Usually provided between the body of the dispenser and the end of the hatch opposite to the hinging end are engagement/disengagement means, which can be operated manually by the user.
This second type of solution enables the problems of poor practicality mentioned previously in relation to the dispensers provided with removable plugs to be overcome. In order to gain access to the charging passage, in fact, the user simply has to tip the aforesaid hatch, with the hatch itself that remains in any case physically joined to the body of the dispenser.
If this type of solution on the one hand facilitates to some extent the activity of topping-up of the reservoir with the liquid washing agent, on the other hand it does not prove completely efficient and reliable. The hatch has in fact the points of hinging and engagement in closing that are at a distance from one another (typically at the two opposite ends of the hatch), as well as at a distance from the sealing region provided by the gasket, which is mounted in the intermediate part of the hatch. This configuration, together with the typical reduced thickness (approximately 2 mm) of the body made of plastic material of the hatch, can give rise to non-uniform bending and/or yielding and/or compression of the gasket resting on the corresponding sealing surface. The solutions using hatches are moreover less reliable in the long run, precisely on account of degradation in the quality of the seal provided by the gasket. It is to be considered also that the body of the hatch, which is thin and made of plastic material, is subject over time to innumerable thermal cycles. This can give rise to deformations of the hatch, which, albeit minimal and even only temporary, adversely affect the quality of the seal in an area corresponding to the passage for charging the reservoir.